GB2135473A

GB2135473A - Fibre optics element

Info

Publication number: GB2135473A
Application number: GB08304623A
Authority: GB
Inventors: James Walter Rawson
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-18
Filing date: 1983-02-18
Publication date: 1984-08-30
Also published as: GB8304623D0

Abstract

A fibre optic element to convey light and having an inclined end face (CT) whereby said light also passes through a sidewall (FS) of the fibre optic element. The sidewall may be flat, as shown, to not refract light, or curved (Figure 2 not shown) to cause the light to converge or diverge. The reflectivity of the inclined end face may be enhanced eg by deposition of silver or aluminium thereon. The element has applications in sewing machines eg. to monitor thread feed or position of the edge of a piece of material. <IMAGE>

Description

SPECIFICATION Fibre optics element This invention relates to fibre optics elements.

Fibre optics elements are now well-known for their ability to convey light along an axial path through the element, such as a rod or fibre, with very low loss of light intensity. Techniques for improving the transmisssion quaiity by use of materials of different refractive indices, e.g. clad rods or fibre, and for making connections between rods are well-known. In such connections care is taken to cut or "cleave" the rod cleanly and form a flat face perpendicular to the axis of the rod by polishing if needed. The rods, when fine enough, can be bent into a curve to take light "round a corner" without significant extra loss in amplitude however the rod must end up with its axis pointing in the direction in which the light is to enter or leave the rod.

It is an object of the invention to provide a fibre optic element in which the direction in which light, or other similar radiation, enters or leaves is not so constrained.

According to the invention there is provided a fibre optic element to convey light and having an inclined end face whereby said light also passes through a sidewall of the fibre optic element.

The light may enter of leave through the sidewall.

The sidewall may be flat to not refract the light.

The sidewall may be curved to cause the light to converge, e.g. to a focus, or to cause the light to diverge, e.g. into a fan in a plane. An additional lens may be used.

The inclined end face may be "silvered" e.g. by depositing silver or aluminium, to improve its reflectivity.

The element may be included in a device to monitor the action of a sewing machine or other textile machine.

The device may monitor thread feed or the position of the edge of a piece of material.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figures 1, 2 and 3 show different fibre optic elements embodying the invention, and Figures 4 and 5 show arrangements to monitor the edges of fabric.

Figure 1 shows the end part of a clad glass rod GR. The part not shown can be as long as required, subject to light loss, and the remote end may be placed adjacent to a light source. The end of the rod GR is not cut square but at an angle to produce a cut face CT. This face is cut so that light in the rod is reflected out of the side of the rod along light path LP. The clad glass rod GR can be a piece of fibre optic material about 3 mm in diameter. The cut face CT can be formed by grinding. The cut face must be smooth to reduce scatter of light. Generally it will be essential to polish the unit face CF to produce a suitable finish. As shown in Figure 1 the side of the rod FS is made plane so that light emerges without being bent or curved glass or glass layers of different refactive index.However some scatter and multiple reflection can still occur inside the end part of the element, so the light may not emerge as a parallel beam. A lens or other device, such as a slit, may be fitted to face FS to collimate the light to produce a more uniform beam of light. An additional lens may also be used to focus the light, with or without a collimator. In this way a substantially parallel beam can be obtained if required.

The rod in Figure 2 forms a lens for the sideways radiated light so that the light can be concentrated at a selected position, F.

The proportion of the light in the rod reflected sideways out of the rod depends on the reflectivity of the cut face CT. This in turn depends on the exact angle of the face to the rod axis and any coating on the face. The angle must also be determined with reference to the diameter of the fibre as well as the wavelength of the light, or similar radiation e.g. in infra-red, that is to be used. It has been found by experiment that the angle is best set to within +20 of a specific value to obtain consistant results for a given group of conditions.

The coating can also be determined by experiment. Black, white, silver and aluminium coatings have been tried. A black paint coating reflects about 40% of the light in the rod. A white paint coating reflects about 75%. Pure silver deposited by the traditional method gives about 90% reflectivity and aluminium brushed on or sprayed on gives about 60% reflectivity or better, The surface finish, i.e. the polishing of the ground cut face CT is crucial.

When the curved wall is used as a lens, to converge the light with a convex lens as in Figure 2 or even to diverge the light by forming a concave lens, not shown, the action again depends on the wavelength of the light and the diameter of the fibre.

The ability to direct a light beam of controlled fprm at an angle to the path along which the light is supplied is of considerable value when light is to be applied in confined spaces e.g. to illuminate an area as part of a monitoring arrangement to project a beam in a particular direction. The technique of bending the rod is limited in application because the minimum radius of curvature is quite large and causes the rod to occupy significant volume.

Figure 3 shows fibre optic elements with two oppositely inclined cut faces CT1, CT2 and respective flat surfaces FS1, FS2. More than two such cut faces may be provided on the rod, which need not be rectangular in cross-section.

As described in co-pending Patent Application entitled Monitoring Textile Thread (our reference 123903) the above fibre optic element can be used to provide a light beam for a thread monitor but many other applications are possible, for example to monitor the position of the edge of a piece of material, as used in copending Patent Application entitled Thread Monitoring in Textile Machines (our reference 125361).

One specific dimension has been mentioned above, viz 3 mm diameter rod, and an angle for the cut face of around 450 has been found suitable but clearly other dimensions and angles can be used as appropriate. For example if a larger amount of illumination is required a larger diameter rod is needed. The rod may be round, square, rectangular or of other appropriate crosssection.

Figure 4 shows in schematic elevation an arrangement using rods of rectangular crosssection by which fabric can be monitored. Three rods are used R1, R2, R3. Rods R1 and R2 have single inclined, polished cut faces, generally as described above, across the larger cross-sectional dimensions of the rods. (The smaller dimension of the rods is seen in the Figure). The rod R3 has two inclined polished cut faces each as described above but with opposed inclination, each cut face occupying half of the larger dimensions of the rod, similar to the form of Figure 3. The rods are stacked as shown in a spaced relationship. Light is supplied to the remove end (not shown) of rod R3 and emerges, after reflection at one or other cut face, in a respective direction at right angles to the rod R3. Each direction is towards one of the rods R1, R2.Light from rod R3 falling on rods R1, R2 is reflected at the respective cut face to be conveyed along the rod to the remote end (not shown). A suitable detector is provided at these remote ends of rods R1, R2.

In use fabric layers FL1, FL2, are passed as shown between rods R1 and R3 and R2 and R3. If one or both fabric layers is absent light supplied to rod R3 reaches the respective detector. The detector is arranged to provide a signal indicative of the presence or absence of a fabric layer.

Conveniently two distinct wavelengths of light are supplied to rod R3 and an individual detector for one of the waveiengths is provided on rod R1 and for the other wavelength on rod R2. In this way better discrimination can be achieved. The light may be visible or infra red as appropriate.

The source of light for rod R3 and the detectors for rods R1, R2 may be semi-conductor devices, as are well-known in the art. Pulse position modulation of the light may be used.

In a particular application to an industrial sewing machine the rods are installed in a folder or guide by which one or more fabric layers or strips are fed to the sewing position. The detector information is applied to a suitable monitor device so that the operator can be made aware of a loss of fabric feed. This may be the end of a piece of fabric or the displacement of the fabric to one side so that it is not fed correctly. To reduce obstruction in the sewing position light may be conveyed to and from the rods by flexible fibre optic elements, such as size 1 fibre, connected to the rods and curved away towards the drive end of the machine.

The monitor device may be local to one machine or remote and deal with several machines, each equipped as first described.

For one particular application monitoring trim supply each rod R1, R2, R3 is about 1 mm thick and 5 mm wide.

Figure 5 shows another form of fabric edge detector embodying the invention. A brass body is machined to form three overlaid plates projecting from a block having bones, one for each plate, in which fibre optics elements can be placed. The brass body is sized and shaped to be convenient for use by a sewing machine operator just in front of the needle as a feed for several layers of fabric which have to be sewn together. With the block form shown the fibre optics elements would emerge towards the main part of the machine and away from the sewing area.

The upper and lower fibre optics elements, UF, LF, are each formed from a length of image conduit with an inclined outer end and a straight cut inner end. The inner end abuts the end of the bundle of fine fibre optics which extend to a semiconductor sensor at a remote point. The junction of the conduit and bundle are sheathed in a stainless steel tube and then in a brass outer tube having a lengthwise slot. The brass tube fits into a bore in the block and a grub screw is used to lock the fibre optics element in position by engaging the lengthwise slot. The inclined ends of the upper and lower conduits are placed one above the other to face towards each other. The central brass plate has a slot filled with a "PERSPEX" (RTM) material incorporating particles to diffuse light out of the slot.There is a fibre optic bundle to convey light to the PERSPEX-filled slot to be radiated towards the upper and lower fibre optics elements.

The arrangement is such that the presence or absence of fabric can be monitored, and a fault condition detected, by semi-conductor detector elements at the remote ends of the upper and lower fibre optics bundles. The level of illumination from the PERSPEX material can be adjusted to suit opacity of the fabrics.

If required more elements can be used to check that the edge of the fabric is correctly aligned to a chosen line. These elements are adjustable, use the lengthwise slots and grub screw, to define the acceptable path for the fabric edge.

The fibre optic bundles can be of Y-form if required.

The sheath on the image conduit can be slotted at the outer end and filled with PERSPEX while the cavity beyond the inclined face can be filled with black epoxy to complete the enclosure of the optics.

Instead of receiving the light on the outer elements these can be used to transmit light to a central element which conveys the light to a remote receiver and detector arrangement.

The various fibre optic elements have been described in the context of and as of a size suitable for industrial sewing machines but clearly other sizes may be used for other applications.

Claims

CLAIMS (Filed on 4 July 1983)

1. A fibre optic element to convey light and having an inclined end face whereby said light also passes through a sidewall of the fibre optic element.

2. An element according to Claim 1 in which the light may enter or leave through the sidewall.

3. An element according to Claim 1 or Claim 2 in which the sidewall is flat to not refract the light.

4. An element according to Claim 1 in which the sidewall is curved to cause the light to converge, e.g. to a focus, or to cause the light to diverge, e.g. into a fan in a plane.

5. An element according to Claim 1 or Claim 5 together with an additional lens.

6. An element according to Claim 1 in which the inclined end face has an enhanced reflectivity e.g. by depositing silver or aluminium.

7. A device including an element according to any one of Ciaims 1 to 6 arranged to monitor the action of a sewing machine or other textile machine.

8. A device according to Claim 7 in which the device is arranged to monitor thread feed or the position of the edge of a piece of material.

9. A fibre optic element substantially as herein described with reference to the accompanying drawings.

10. A device to monitor a sewing machine substantially as herein described with reference to one or more of Figures 3, 4 and 5 of the accompanying drawings.